Circuit arrangement for producing a comparatively high voltage utilizing voltage dependent resistors



N 1965 G. H. P. ALMA ETAL 3,217,236

CIRCUIT ARRANGEMENT FOR PRODUCING A COMPARATIVELY HIGH VOLTAGE UTILIZINGVOLTAGE DEPENDENT RESISTORS Filed May a. 1961 FIG. 2

INVENTOR GERRIT H.P.ALMA. WILLEM BUSSCHER.

BY i AG T United States Patent 3,217,236 CIRCUIT ARRANGEMENT FORPRODUCING A COMPARATIVELY HIGH VOLTAGE UTILIZING VOLTAGE DEPENDENTRESISTORS Gerrit Hendrik Petrus Alma and Willem Busscher, Eindhoven,Netherlands, assignors to North American Philips Company, Inc., NewYork, N.Y., a corporation of Delaware Filed May 3, 1961, Ser. No.107,483 Claims priority, application Netherlands, June 24, 1960, 253,08211 Claims. (Cl. 323-22) This invention relates to circuit arrangementsfor stabilizing a voltage by means of a ballast tube connected inparallel with the load on the circuit arrangement and controlled inopposite sense to, and dependently upon, the variations in the saidload.

Such circuit arrangements are often used in television receivers forproducing the high voltage for supplying the final anode of the picturetube. The high voltage is stabilized by means of the ballast tube sothat variations in the beam current through the display tube, whichconstitutes the load for the circuit arrangement, do not producevariations in the high voltage produced.

However, the use of such a ballast tube has the disadvantage that itmust be capable of dissipating a high power, since with the beam currentcut off the full power delivered by the high voltage circuit must bedissipated by the ballast tube.

In addition, the full high voltage is set up across the ballast tubewhich must therefore be rated for a high breakdown voltage.

The foregoing requirements necessitate the use of a tube having verylarge dimensions. Due to its large bulb, the tube differs from the kindof tubes normally employed so that such bulbs would have to bemanufactured either by hand, or on a special machine. Furthermore, thedimensions of the electrodes differ greatly from those of tubes normallyemployed and the manufacture of such a ballast tube would thus becomeextremely expensive.

In order to obviate these disadvantages, a circuit arrangement accordingto the invention is characterized by the addition of a voltage-dependentresistor connected in series with the anode of the ballast tube.

In order that the invention may be readily carried into efiect, apossible embodiment of a circuit arrangement according thereto will nowbe described in detail, by way of example, with reference to theaccompanying diagrammatic drawing, in which:

FIGURE 1 is a circuit diagram of one embodiment of the invention; and

FIGURE 2 shows a desired anode current-grid voltage characteristic of aballast tube as used in the circuit of FIGURE 1.

In FIGURE 1, tube 1 constitutes the output stage of a line-deflectioncircuit in a television receiver. The control grid of tube 1 has appliedto it a control voltage 2 which periodically releases tube 1. The anodecircuit of the tube 1 includes a line-output transformer 3 comprising aprimary winding 4 and a secondary or high voltage winding 5. Connectedto a tapping on the primary winding 4 is the cathode of a series-boosterdiode 6, the anode of which is connected to the positive terminal of avoltage source delivering a supply voltage of V volts. One end of theprimary winding 4 is connected to one electrode of a capacitor 7, theother electrode of which is also connected to the positive terminal ofthe voltage source. As is well-known, the capacitor 7 is associated withthe circuit of the series-booster diode and a positive direct voltageconsiderably higher than the supply voltage V is set up at the junctionpoint of the capacitor 7 and the primary "ice winding 4. Also connectedto the primary winding 4 is a line-deflection coil 8 which is traversedby the sawtooth deflecting current produced, by means of which the beamcurrent through the picture tube 9 is deflected in a horizontaldirection.

The pulses produced during the fiy-back period of the sawtooth currentare stepped up by means of the Winding 5. A rectifier diode 10 isconnected to the free end of the high voltage winding 5 and rectifiesthe pulses resulting in a high voltage V which serves to feed the finalanode of the display tube 9.

As is well-known, the beam current through the picture tube 9 may varyin several ways. This may be effected, on the one hand, by means of thevideo-signal which, in the present example, is supplied through avideo-output tube 11 to the cathode of the display tube 9 or, on theother hand, by varying the bias potential at the Wehnelt cylinder 12 foradjusting the background brightness of the picture reproduced by thepicture tube 9.

A high voltage generator as described above for developing a highvoltage V always has a comparatively high internal resistance, forexample, in the order of 4 or 5 M9. Variation in the beam current wouldthus result in varition of the voltage V produced. This is undesirable.More particularly, in colour-television receivers, such variation in thehigh voltage V results in color distortion because the convergencecircuits, which are always present in a colour-television receiver, nolonger operate satisfactorily.

It is known, in order to stabilize the high voltage V,,, to connect aballast tube 13 in parallel with the picture tube 9 and to control thistube so that upon an increase in beam current, the current through theballast tube decreases, and conversely, so that the sum of the twocurrents remains substantially unchanged under all conditions.Consequently, the voltage drop across the internal resistance of thevoltage source V also remains unchanged despite the variations in beamcurrent.

The ballast tube 13 may be controlled, for example, by means of anetwork comprising a resistor 14 and a capacitor 15 connected betweenthe primary winding 4 and the secondary winding 5. The resistor 14 isthen traversed by the direct current I from the high voltage circuit sothat the voltage drop across the resistor 14 is a measure of the saiddirect current or load current I The capacitor 15 serves to pass thepulses to the secondary winding 5.

The cathode of the ballast tube 13 is connected to the junction ofwinding 4 and capacitor 7 and the control grid is connected, through asmoothing resistor 16, to the junction point of resistor 14 and winding5 and, through a smoothing capacitor 17, to the cathode.

As previously mentioned, a positive direct voltage is set up across thecapacitor 7 and the resistor 14 must therefore be so proportioned thatthe voltage drop across it is higher than that across the capacitor 7 sothat the control grid is, under all conditions, negative relative to thecathode.

FIGURE 1 also shows a stabilizing circuit 18 which is controlled from atapping 19 on the primary winding 4 and which develops a negativecontrol-voltage which is applied through a resistor 20 to the controlgrid of the lineoutput tube 1. The stabilizing circuit 18 serves to stabilize the sawtooth current through the deflection coil 8 and thevoltage across the capacitor 7 in the event of variation in the supplyvoltage V or in case of ageing of the tubes 1 and 6, and in case oftemperature variations. If the load on the high-voltage circuit wouldnot vary, the high voltage V would thus also remain constant. Thepurpose of ballast tube 13 is to stabilize the voltage V against loadcurrent variations.

If the ballast tube 13 were connected directly between the cathode ofthe rectifier diode 10 and the positive terminal of the supply voltagesource, substantially the full high voltage would be set up across theballast tube 13. In fact, V is many times smaller than V so that V isnegligible relative to V Assuming, for example, that V =25 kilovolts, avoltage of 25 kilovolts would be set up across the ballast tube whichwould thus have to be rated for a breakdown voltage higher than thisvalue. This is a very stringent requirement and, in addition, thisrequirement must be made irrespective of the current traversing theballast tube 13.

In addition, the ballast tube 13 must be capable of dissipating thepower supplied by the high-voltage circuit when the beam current throughthe picture tube 9 is cut off (black level). Assuming that the currentthen flowing through the ballast tube 13 is about 1 rna., it isnecessary for the tube to dissipate 25 watts. This requirement also ishigh.

The foregoing implies that a very large tube would be required which isdiflicult to construct. In addition, because of its large bulb, such atube differs from the kind of tubes normally employed so that such bulbswould have to be manufactured either by hand, or on a special machine.As a matter of fact, the electrodes, too, differ from those of the tubesnormally employed so that it will be evident that the manufacture ofsuch a ballast tube would become extremely expensive.

A first improvement may be obtained by including a series-impedance inseries with the ballast tube 13. Maintaining a constant load current assuch is not influenced thereby since control of the ballast tube 13ensures that the direct current delivered by the high-voltage circuitremains substantially unchanged irrespective of the intensity of thebeam current through the picture tube 9.

If, for example, an ohmic resistor R of 22 megohms is chosen as theseries impedance, it follows from Table I that the maximum dissipationof the ballast tube 13 is reduced from 25 watts to 7.1 watts. Thismaximum dissipation occurs for a current of about 0.56 ma.

Table I [With a series-resistor R of 22 megohms] I ballast, vtuba, kv.Vr, tubey ma. watts 1. 3. O 22. 0 3. 0 0. 56 12. 12. 5 7. 1 O. 50 14. 0I1. 0 7. 0 U. 25 19. 5 5. 5 4. q 0. 1O 22. 8 2. 2 2. 3 0. 00 25. U 0. O00. 0

A considerable improvement however is obtained if, according to theinvention, instead of an ordinary linear resistor, a voltage-dependentresistor 21 (a so-called V.D.R. resistor) is connected in series withthe ballast tube 13, as shown in FIGURE 1.

Table II In fact, from Table II it appears that the maximum dissipationof the ballast tube 13, which now occurs for a current of about 0.96rna., is reduced to 3.84 watts, which is again much less than the 7.1watts for which the ballast tube must be rated when using a linear orohmic resistor.

According to the invention, a further improvement may be obtained if thecurrent through the ballast tube is controlled back to a predeterminedminimum value of I amp. instead of a value zero for the maximum beamcurrent. Assuming that 1 :01 rna., it follows from Table I that themaximum voltage set up across the ballast tube 13 is about 22.8kilovolts when using an ohmic resistor of 22 megohms, and from Table IIthat this maximum voltage drops to 10 kilovolts when using avoltage-dependent resistor 21.

From the above it follows that by using the two steps, that is to say:

(1) Connecting in series a votlage-dependent resistor 21 (2) Preventingthe current through the ballast tube 13 from decreasing below a value ofI amp.

the dissipation requirement is reduced from 25 watts to about 3.84 wattsand the breakdown-voltage requirement from 25 kilovolts to 10 kilovolts.

It has thus become possible considerably to reduce the dimensions of theballast tube 13 to the size which is common practice for ordinarytelevision receiver tubes.

In the present example, in which a triode is chosen as the ballast tube13, the voltage drop across the voltagedependent resistor 21 is set to22 kilovolts for a current of 1 ma. through the ballast tube 13.

This is obtained in that the voltage-dependent resistor 21, theproperties of which may be written by the formula V Cl" (1) isproportioned so that the constants C and ,8 are given y C=82(10 )S2- and3:0.19

By increasing C, it is possible to reduce the maximum dissipation of thetube 13, which may be calculated with the aid of the formula =i. 2 tubamax. h

The voltage across the ballast tube 13 is given by V V -CI If I becomessmaller, it follows from Formula 3 that the voltage across the tubeincreases. Consequently, the maximum voltage across the tube 13 occursfor the minimum permissible current I so that it will be evident thatthis maximum voltage may be decreased by increasing the constant C ofVDR 21.

Both the maximum dissipation and the breakdown voltage for which theballast tube must be rated may be decreased by increasing C. However, inthis case, the anode voltage is also smaller during the occurrence ofthe maximum current. A further increase of the constant C may thereforegive rise to a situation in which the maximum anode current can nolonger flow due to the reaction of the anode voltage upon the anodecurrent (penetration factor), unless the negative grid-bias isexceptionally decreased, thus involving a risk of unwanted grid current.

The foregoing may be avoided by using a screen-grid tube instead of atriode as the ballast tube so that the current control is solelydetermined by the voltage at the control grid despite the high value ofthe voltage-dependent resistor 21. In fact, as is well-known, the anodecurrent of such a screen-grid tube is much less dependent upon the anodevoltage than in the case of a triode. (The screen-grid tube used may be,for example, a tetrode or a pentode.) If the cathode of the ballast tube13 is connected to the lower side of the capacitor 7, then the screengrid may be connected to the junction point of the primary winding 4 andthe capacitor 7, as illustrated in FIG. 1, for obtaining the desiredsupply voltage. As an alternative, it would be possible to connect thecathode of the ballast tube to earth and to connect the screen grid tothe ordinary supply voltage of V volts.

It will also be evident that if the current through the ballast tubemust not drop below I ampere, the maximum current traversing it mustalso be slightly increased with respect to the case in which the ballasttube 13 is completely cut off when the beam current through the picturetube 9 is at maximum.

In the example shown, this implies that I must be raised from 1 ma. to1.1 ma., if 1 :01 ma. From this it follows that if the beam currentthrough the picture tube 9 is 1ma., the current through the ballast tube13 assumes a value I =0.1 ma., and if the beam current is cut off, thecurrent through the ballast tube 13 is about 1.1 ma. It is thereforeensured that the sum of the two currents is, under all conditions, about1.1 ma. so that the voltage drop across the internal resistance of thehigh voltage circuit always remains constant and hence the value of thehigh voltage V produced does not substantially vary despite variationsin the beam current.

The following step may be taken to prevent the current through theballast tube 13 from decreasing below the value 1 The resistor 14 may beso proportioned that the voltage at the control grid of the ballast tube13 never decreases below the cut-ofi voltage even for the maximum beamcurrent possible through the picture tube 9.

However, it is preferable for the ballast tube 13 itself to beconstructed so that the anode current I cannot decrease below a value 1irrespective of the extent of the increase in negative grid-bias V atthe control grid of this tube. This is illustrated in FIGURE 2, whichshows a desired I V characteristic of the ballast tube 13. As can beseen from this figure, the mutual conductance of tube 13 becomessubstantially zero when the control-grid voltage reaches the value V bywhich an anode current of I ampere keeps flowing.

Such a characteristic may be obtained, for example, by providing thecontrol grid with one or more additional apertures. For this purpose,one or more turns may be omitted in winding the grid wire so that, as itwere, a diode which continuously conveys a current I is connected inparallel with the ballast tube proper. The same result could beobtained, for example, by connecting a fixed resistor in parallel withthe ballast tube 13. When the ballast tube is completely cut off, thisresistor is traversed by the current I In the example shown, the controlgrid is wound so that the grid voltage indicated in FIGURE 2 is Thisaffords the advantage that I is determined by the tube itself so thatwith a correct choice of the associated voltage-dependent resistor 21the requirement for the maximum permissible breakdown voltage isfulfilled, otherwise the choice of the resistor 14 would also play apart.

In conclusion, it is mentioned that the stabilizing circuit 18 is notstrictly necessary. If it is desired to take only the variations in beamcurrent into account, a control circuit with the ballast tube 13 alonesufiices.

In addition, the use of the circuit arrangement need not be limited totelevision receivers. The inventive concept may be used in all thosecases where a voltage is produced which is stabilized by means of aballast tube. In fact, such circuit arrangements may also be used forstabilizing the high voltage in X-ray equipment and radar installations.

What is claimed is:

1. A voltage regulating circuit comprising a source of voltage havingfirst and second terminals, load circuit means connected between saidterminals, a ballast device having at least output, common and controlelectrodes, 21 voltage-dependent resistor, means serially connectingsaid resistor and the output-common electrode path of said devicebetween said terminals, and means connected to said control electrodefor controlling the current through said path in the opposite sense withrespect to current in said load circuit means.

2. A voltage regulating circuit comprising a source of voltage havingfirst and second terminals, load circuit means connected between saidterminals, an electron discharge device having at least cathode, anodeand control grid electrodes, a voltage-dependent resistor, meansserially connecting the cathode-anode path of said discharge device andsaid voltage-dependent resistor between said first and second terminals,means for deriving a voltage dependent upon current through said loadcircuit means, and means applying said dependent voltage to said controlgrid electrode whereby current through said discharge device varies inthe opposite sense with respect to current in said load circuit means.

3. A voltage regulating circuit comprising a source of voltage of highimpedance, a load circuit connected to said source, an electrondischarge device having at least cathode, control grid and anodeelectrodes, 21 voltage-dependent resistor, means serially connectingsaid resistor and the anode-cathode path of said device in parallel withsaid load circuit, means for deriving a voltage dependent upon currentflow in said source, and means for applying said dependent voltage tosaid control electrode whereby current variations in said load circuitproduce current variations in the opposite sense in said device.

4. A voltage regulating circuit comprising a source of voltage of highimpedance, a load circuit connected to said source, an electrondischarge device having at least cathode, control grid and anodeelectrodes, a voltage-dependent resistor, means serially connecting saidresistor and the anode-cathode path of said device in parallel with saidload circuit, means for deriving a voltage dependent upon current flowin said source, means for applying said dependent voltage to saidcontrol electrode whereby current variations in said load circuitproduce current variations in the opposite sense in said device, andmeans for maintaining a predetermined minimum current flow in saidresistor.

5. The circuit of claim 4, in which said means for maintaining apredetermined minimum current comprises resistor means connected betweensaid anode and cathode electrodes.

6. The circuit of claim 4, in which said means for maintaining apredetermined minimum current comprises aperture means in said controlgrid electrode whereby anode current flow in said tube is maintainedwhen said control grid electrode has a sutficiently low potential toreduce the transconductance of said device to zero.

7. A high voltage regulating circuit comprising a transformer having aprimary and a secondary winding, means for providing a periodic currentflow in said primary winding, a first series circuit comprising saidprimary winding, resistance means, and said secondary winding in thatorder, a second series circuit comprising serially-connected rectifiermeans and load means, means connecting said first and second seriescircuits in parallel, an electron discharge device having at leastcathode, control grid and anode electrodes, a third series circuitcomprising a voltage-dependent resistor and the cathode-anode path ofsaid device, means connecting said third series circuit in parallel withsaid load means, and means connecting the junction of said resistancemeans and secondary Winding to said control grid electrode, wherebycurrent in said cathode-anode path varies in the opposite sense withrespect to current flow in said load means.

8. A high voltage regulating circuit comprising a transformer having aprimary and secondary winding, means for providing a periodic currentflow in said primary winding, a first series circuit comprising saidprimary winding, resistance means, and said secondary winding in thatorder, a second series circuit comprising serially-connected rectifiermeans and load means, means connecting said first and second seriescircuits in parallel, an electron discharge device having at leastcathode, control grid and anode electrodes, a third series circuitcomprising a voltage-dependent resistor and the cathode-anode path ofsaid device, means connecting said third series circuit in parallel withsaid load means, means connecting the junction of said resistance meansand secondary winding to said control grid electrode, whereby current insaid cathode-anode path varies in the opposite sense with respect tocurrent flow in said load means, and means for maintaining apredetermined minimum current flow in said third series circuit.

9. The circuit of claim 8, in which said device is a screen grid tube.

10. A voltage regulating circuit comprising a source of voltage havingfirst and second terminals, load circuit means connected between saidterminals, a ballast device comprising first and second electrodesdefining a current path through said device and a control electrode, anonlinear voltage-dependent resistor, means serially connecting saiddevice current path and said voltage-dependent resistor between saidfirst and second terminals, means for deriving a control voltage whichvaries with the magnitude of the current flow in said load circuitmeans, means for applying said control voltage to said control electrodein a sense to control the current through said path in the oppositesense with respect to current in said load circuit means, and means formaintaining a predetermined minimum current flow in said resistor.

11. A voltage regulating circuit for a high impedance source of highdirect voltage, said source including a pair of terminals, comprising aload circuit connected across said terminals, an electron dischargedevice having a control electrode and an anode and a cathode whichdefine a current path through said device, a bidirectional non-linearvoltage-dependent resistor, means serially connecting the anode-cathodepath of said discharge device and said voltage dependent resistor acrosssaid terminals, means for deriving a direct voltage which varies withthe total load current supplied by said source, means for applying saiddirect voltage to said control electrode in a sense such that currentvariations in said load circuit produce current variations in theopposite sense in said device, and means serially connected with saidvoltage-dependent resistor for maintaining a predetermined minimumcurrent flow in said resistor.

References Cited by the Examiner UNITED STATES PATENTS 2,534,559 12/50Prince 323--38 X 2,817,055 12/57 Taubenslag et a1. 323-30 X 2,833,8695/58 Ward 328142 X 2,944,186 7/60 Boekhorst et al 31527 3,061,757 10/62Janssen et a1 315-27 FOREIGN PATENTS 210,398 9/57 Australia.

LLOYD MCCOLLUM, Primary Examiner.

ARTHUR GAUSS, MILTON O. HIRSHFIELD,

Examiners.

1. A VOLTAGE REGULATING CIRCUIT COMPRISING A SOURCE OF VOLTAGE HAVING FIRST AND SECOND TERMINALS, LOAD CIRCUIT MEANS CONNECTED BETWEEN SAID TERMINALS, A BALLAST DEVICE HAVING AT LEAST OUTPUT, COMMON AND CONTROL ELECTRODES, A VOLTAGE-DEPENDENT RESISTOR, MEANS SERIALLY CONNECTING SAID RESISTOR AND THE OUTPUT-COMMON ELECTRODE PATH OF SAID 